High current level interrupter means



Aug. 10, 1965 B. FISK ETAL 3,200,260

HIGH CURRENT LEVEL INTERRUPTER MEANS Filed Aug. 29, 1961 HIGH CURRENT UTILIZATION M EA NS INVERTER ANS CURRENT AMPLIFIER Fl LTER- SHAPER TER M EANS INVENTORS BERT FISK MORTON FISCHMAN THEODORE J. RAUEN I AQMXW4 AL-W ATTORNEY LOW CURRENT INTERRUP United States Patent 3,200,260 HIGH CURRENT LEVEL INTERRUPTER MEANS Bert Fisk, Washington, D.C., and Morton Fischman,

Silver Spring, and Theodore J. Rauen, Suitland, Mai,

assignors to the United States of America as represented by the Secretary of the Navy Filed Aug. 29, 1961, Ser. No. 134,786 3 Claims. (Cl. 307-885) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates in general to current interrupter means and in particular to such interrupter means wherein radio frequency interference is minimized.

It is Well recognized in the art that high current level interrupters of the type employed in transmitter keying operations are generally characterized by a large amount of radio frequency interference during the operation thereof and that such radio frequency interference often disrupts reception of intelligible information in the immediate area, the extent of disturbance being a function of the degree of arcing at the interrupter contacts.

Such radio frequency disturbance often affects the operation of other types of radio frequency sensitive equipment such as galvanic instruments, alarm systems and the like. It will be appreciated that deceptive recordings and alarms can readily predicate serious if not disastrous results and that all possible sources of radio frequency interference must be avoided wherever possible when radio frequency sensitive equipment is in the vicinity. A

Numerous techniques to suppress radio frequency interference have been employed in the past with varying degrees of success. Largely, these prior art techniques have required bulky, heavyweight equipment items which, of course, rules out the use of these techniques in miniaturization applications Where both size and weight are crucial factors.

Accordingly, it is an object of this invention to provide a miniaturized high current interrupter means which produces a minimum amount of radio frequency interference during the operation thereof.

It is another object of this invention to provide a miniaturized high current interrupter means of high reliability which may be utilized in remote unattended applications.

It is still another object of this invention to provide a miniaturized high current interrupter means wherein the safety hazard to personnel operating the interrupter means is reduced.

It is a further object of this invention to provide a miniaturized high current interrupter means embodying transistor circuitry and adaptable to space satellite applications.

Other objects of this invention will become apparent upon a mor-e comprehensive understanding of the invention for which reference is had to the following specification and drawings wherein:

7 FIG. 1 is a block diagram of the device of this invention in one embodiment thereof.

FIG. 2 is a schematic diagram of the embodiment of FIG. 1.

3,269,260 Patented Aug. 10, 1965 Briefly, the device of this invention is a high current level transistorized interrupter means wherein the interrupting action normally responsible for radio frequency interference is accomplished at a much lower current and voltage level and the adverse arcing effect is minimized. The invention incorporates several safeguards which insure that the device will function properly irrespective of transistor characteristic variations.

Referring now to the drawings:

In FIG. 1 a transistorized low level teletype keyer for current interruption use, for example, in teleprinter distributor or keyboard systems, at 60 milliamperes current level is shown in block diagram. The depicted embodiment incorporates a low current interrupter means 11 which controls the operation of high current utilization means 12 by means of a first filter-shaper circuit 13, a current amplifier stage 14, an inverter stage 15, second filter shaper means 16 and the emitter follower stage 17 While many approaches to the problem of reducing radio frequency interference due to high current arcing have been attempted in the past utilizing conventional components such as vacuum tubes, mechanical relays, etc, few if any, systems have been devised which embody semiconductor devices. A major obstacle to the use of semiconductor devices has been the factor of internal leakage, which varies with aging, ambient conditions, voltage variations and the like.

In overcoming this obstacle, the present invention utilizes low leakage semiconductor devices and in addition, incorporates several leakage compensation means, for example, a unique bias means, indicated at 18 in FIG. 1, to compensate for semiconductor characteristic changes. By the use of such semiconductor devices and by such compensation, a positive action only in response to intended current interruption is assured.

In FIG. 2, the low current interrupter means is shown as a simple telegraph key 21 and a filter-shaper circuit comprising the resistance 22, 23 and the capacitances 24, 25 is connected directly across the key 21. Thus as the contacts of the key 21 open and close, the resistors 22, 23 limit the surge of current due to the capacitance of the wiring and the associated capacitors 24, 25 serve to bypass to ground any high frequency components which may be generated. As will be explained in more detail hereinafter the resistances 22, 23 and the capacitances 24, 25 act to suppress radiation and also provide shaping of the signal. It will be appreciated that the resistances 22, 23 should be mounted directly across the contacts with the shortest possible leads and that the capacitors also should have short leads, particularly to ground. Further it will be appreciated that one surge resistance may be employed in place of the two resistances shown in the drawing, if desired and that in other instances, the capacitors may be omitted. In a typical embodiment, the resistances 22, 23 might be 22,000 ohms each and the capacitances 24, 25 might be 0.03 mfd. ceramic disc capacitors.

The filter-shaper described above is connected to a high impedance low level amplifier, the NPN transistor 2-5 and associated circuitry, via the shielded cable indicated at 27. V

In a mark condition (contacts of key 21 closed), the base of transistor 26 is driven by approximately microamperes. For any given voltage source, this current is determined by the value of resistance 28, for example 22,000 ohms, and the value of the filter resistances 22 and 23. The transistor 26, which for example, might be a 2N340 NPN transistor, amplifies the base current to several hundred microamperes which drives the phase inverter stage, transistor 31 and associated circuitry. In particular, transistor 26 drives the base of transistor 31, which, for example, might be a 2N398 PNP transistor, through the resistance 29, for example, 15,000 ohms.

As will be appreciated, the phase inverter stage is essential to the embodiment discussed in detail herein due to the input pulse polarity requirement of the next stage. In other embodiments, however, such an input pulse polarity requirment might not be involved and obviously, other signal transfer means might be substituted for the phase inverter exemplarily shown in the depicted embodiment.

In the embodiment of FIG. 2, the collector current of transistor 31, about milliamperes, drives the output transistor 41 and associated circuitry, via the RC filtershaper comprised'of resistance 51 and capacitance 52, for example, 5,600 ohms and 0.1 mfd., respectively. The principal function of this filter-shaper is to further shape the signal after amplification and inversion thereof.

In particular, this filter-shaper is provided to shape the trailing edge of each pulse whereas the filter-shaper directly connected across the keyer contacts 21 is provided to shape the leading edge of each pulse. It will be appreciated that this filter-shaper may be omitted in some applications of the device of this invention, particularly in those applications where a lesser assurance of positive action is required.

Transistor 41 is connected as a high current emitter follower and, in the depicted embodiment, is adapted to supply 60 milliamperes to the output load impedance 42. It will be appreciated that the resistance 43, for example,

47 ohms, in the collector circuit of transistor 41 serves to protect the transistor 41 from accidental short circuits between the output (emitter) and ground and may be omitted where other safeguards are provided.

In the embodiment of FIG. 2, the impedance 42 in the emitter circuit of transistor 41 represents the high current utilization means 12 of FIG. 1. It will be appreciated, however, that the high current output transistor 41 may be connected other than as an emitter follower when an external voltage source is employed'to energize the high current path. In such instance the utilization means, might be divorced from the common ground connection shown and the high current path including the transistor 41 and the utilization means 12 might be connected directly across the external voltage source.

In a space condition the open contacts of keyer 21 interrupt the base current of transistor 26 and the emitter bias of approximately one volt, which is determined by resistance 55 (110 ohms), resistance 56 (2,700 ohms), and resistance 28, cuts off the transistor 26.

By reason of the voltage drop across forward conducting diode 61,- for example, silicon type 1N461, which biases the emitter of transistor 31 about 0.1 to 0.7 volt less positive than its base, the transistor 31 also is cutoff when the transistor 26 is not conducting due to the open contacts of keyer 21.

It will be noted that the silicon diode 61 is not employed herein as a unidirectional element in the conventional It has been found that the forward consponges 4 across the diode 61. Consequently, pulses of lesser magnitude will not alter the operational state of transistor 31 and high reliability under extremes of ambient temperature is provided by the incorporation of diode 61. It will be appreciated that such reliability is of particular importance in applications where extraneous noise pulses occur frequently.

With transistor 31 cut-off, the output transistor 41 also will be cut 011 and only a slight leakage current will flow through the load. This leakage current should be minimized and it has been found that satisfactory results, leakage current less than microamperes, may be obtained at normal room temperatures using production variety silicon transistors for transistor 41.

The device of this invention is particularly adaptable to printed circuit assembly. In such assembly, however, heat dissipation means may be limited and it has been found desirable in many instances to provide a suitable heat sink for the high current carrying transistor 41. A piece of aluminum x 1%" x 2 /8" has been found useful for this purpose in such assembly.

In installations where an external'power source is utilized by the keyer and other equipment as well, it has been found desirable to regulate the power source to main-. tain a constant power drain at all times to prevent interference due to voltage source fluctuations.

It will be appreciated that the present invention affords a basic DC current control device which performs a yes-no function, that is, the device has two distinct operating conditions and in each the output current is a set value, for example 60 milliamperes and substantially zero.

The device of the present invention is particularly adaptable to teleprinter equipment, electric typewriters signaling relays and the like. It is readily apparent, however, that the present invention is not restricted to this type of equipment and that it may be adapted to other types of equipment as well. For example, the key 21 might be replaced by a photoelectric switching means which controls a high current apparatus in response to a light condition variation, if desired.

Moreover, it will be appreciated that the types of transistors and the component values referred to in the above description of one embodiment of the invention are merely exemplary and that variation therefrom is clearly with-- much greater current level than a current to be interrupted comprising:

low current interrupter means,

first and second radiation suppressing and shaping means directly connected to said interrupter means with the shortest possible connection,

a bias source,

a first transistor having a base, emitter and collector,

with said base coupled to said first radiation suppressing and shaping means, said emitter coupled to ground, and said collector coupled to said bias source, a

a second transistor having a base, emitter and collector, with said base coupled to said collector of said first transistor, said emitter coupled to the emitter of said first transistor,

biasing means coupling said emitters of said first and second transistors together and to said interrupter means through said second radiation suppressing and shaping means,

a diode coupled between the base and emitter second transistor, and

an emitter follower output transistor having a base, emitter and collector, with the collector coupled to a bias source, said emitter being resistively coupled to ground and said base coupled to the collector of said second transistor.

of said;

2. The circuit of claim 1 wherein said base of said emitter follower is coupled to said collector of said second transistor by means of a filtering and shaping network.

3. The circuit of claim 2 wherein said interrupter includes a first and second contact, and wherein said first radiation suppressing and shaping means includes a first resistor coupled between said first contact and the base of said first transistor, and a first capacitor connected between said base of said first transistor and ground, and wherein said second radiation suppressing and shaping means includes a second resistor coupled between said second contact and the emitters of said first and second transistor, and a second capacitor coupled between said biasing means and ground.

References Cited by the Examiner UNITED STATES PATENTS 6/59 Lindsay 30788.5

30 her 1953, pages 28-30 and 114 (page 30 relied on).

ARTHUR GAUSS, Primary Examiner. GEGRGE N. WESTBY, Examiner. 

1. A KEYER CIRCUIT FOR PRODUCING AN OUTPUT SIGNAL OF A MUCH GREATER CURRENT LEVEL THAN A CURRENT TO BE INTERRUTPTED COMPRISING: LOW CURRENT INTERRUPTER MEANS, FIRST AND SECOND RADIATIONSUPPRESSING AND SHAPING MEANS DIRECTLY CONNECTED TO SAID INTERRUPTER MEANS WITH THE SHORTEST POSSIBLE CONNECTION, A BIAS SOURCE, A FIRST TRANSISTOR HAVING A BASE, EMITTER AND COLLECTOR, WITH SID BASE COUPLED TO SAID FIRST RADIATION SUPPRESSING AND SHAPING MEANS, SAID EMITTER COUPLED TO GROUND, AND SAID COLLECTOR COUPLE D TO SAID BIAS SOURCE, A SECOND TRANSISTOR HAVING A BASE, EMITTER AND COLECTOR, WITH SAID BASE COUPLED TO SAID COLLECTOR OF SAID FIRST TRANSISTOR, SIAD EMITTER COUPLED TO THE EMITTER OF SAID FIRST TRANSISTOR, BIASING MEANS COUPLING SAID EMITTERS OF SAID FIRST AND SECOND TRANSISTORS TOGETHER AND TO SAID INTERRUPTER MEASN THROUGH SAID SECOND RADIATION SUPPRESSING AND SHAPING MEANS, A DIODE COUPLED BETWEEN THE BASE AND EMITTER OF SAID SECOND TRANSISTOR, AND AN EMITTER FOLLOWER OUTPUT TRANSISTOR HAVING A BASE, EMITTER AND COLLECTOR, WITH THE COLLECTOR COUPLED TO A BIAS SOURCE, SAID EMITTER BEING RESISTIVELY COUPLED TO GROUND AND SAID BASE COUPLED TO THE COLLECTOR OF SAID SECOND TRANSISTOR. 